1. Field of the Invention
The present invention relates to communications, and more particularly, to a switch frame, a method of transmitting the same at a mobile station, and a quality indicator channel structure including the same.
2. Discussion of the Related Art
In a 1×EV-DV (1× EV-Data & Voice) system, a reverse-channel quality indicator channel (hereinafter referred to as R-CQICH) has been defined in order to support a high-rate packet data channel.
Briefly, the above-described R-CQICH transmission plays two roles. First, the R-CQICH physical channel is used to report channel quality information that is represented as a power ratio of a carrier-to-interference (hereinafter referred to as C/I) signal of a carrier of the best serving cell/sector for every 1.25 ms. Based on this channel information, a corresponding base transceiver subsystem (base station) varies transmission power levels of a packet data channel, and data transmission rates (for example, encoder packet data sizes and transmission slot durations, when to schedule a particular mobile station on the packet data channel, and when to handoff transmission on the packet data channel from one pilot (e.g., sector or base station (e.g., cell)) to another sector or base station (e.g., cell)).
Second, the CQICH may be used to point the best serving cell/sector among cells/sectors that belong to an active set. That is, since the whole or a portion of the CQICH is transmitted, being covered with a Walsh code of the best cell/sector, the corresponding base station can recognize the best serving cell/sector by decovering the CQICH. This coverage area represents a cell or any one of sectors included in the cell.
In case that no cell/sector switching exists, a transmission protocol of the CQICH is briefly divided into a normal mode and a reduced rate mode. Also, two kinds of transmission modes, that is, a full C/I feedback mode (hereinafter full reporting mode) and a differential C/I (modulation) feedback mode (hereinafter referred to as DM mode) exist with respect to the normal mode and the reduced rate mode, respectively. Further, the full and DM reporting mode are modified by pilot gating (hereinafter as control hold mode).
FIGS. 1A and 1B are diagrams explaining a related art method of transmitting channel information in a normal mode of an active state. FIGS. 2A and 2B are diagrams explaining a related art method of transmitting channel information in a ½ reduced rate mode of an active state. FIGS. 3A and 3B and 4A and 4B show a CQICH transmission mode in the control hold mode.
FIGS. 1A and 1B and FIGS. 2A and 2B are for explaining four kinds of transmission modes in case that no cell/sector switching exists in the transmission protocol of the CQICH, and they show the construction of frames for transmitting channel information (for instance, carrier-to-interference ratio).
The first transmission mode is a DM transmission mode in the normal mode as illustrated in FIG. 1A. In the DM mode of the normal mode, a mobile station quantizes forward full carrier-to-interference (C/I) information of the present serving cell/sector, i.e., the best serving cell/sector measured at a first slot of 1.25 ms for every frame of 20 ms by a predetermined number of bits, applies a [12, 4]-block coding to the quantized full C/I information, and performs a 8-ary Walsh covering with respect to the block-coded C/I information to transmit the Walsh-covered C/I information to at least one base station (BS) in an active set including the BTSs of the best serving cell/sector.
During the 15 remaining slots of 1.25 ms, the mobile station judges whether a C/I quality (e.g., forward link quality) measured at the present slot has been changed to a good quality or a bad quality in comparison to the full C/I information measured at the previous slot, and transmits a quality up/down command (or differential modulation symbol with at least one bit) to the base stations accordingly. This quality up/down command is repeated 15 times, and the 8-ary Walsh covering that corresponds to the best serving cell/sector is applied thereto for its transmission.
The full C/I information and the up/down command can be detected and used only by the base stations that can perform a Walsh decovering of the full C/I information and the up/down command. In the DM mode of the normal mode, which is different from the full reporting mode of the normal mode, the transmission power can be greatly reduced if the number of bits of information to be transmitted for 1.25 ms is one. That is, by using the DM mode of the normal mode, the load of the reverse link can be greatly reduced in comparison to the full reporting mode of the normal mode.
However, the DM mode of the normal mode has the disadvantages that if the corresponding base station cannot detect the full C/I information of the best serving cell/sector received during the first slot period of the 20 ms frame or receives the full C/I information with an error rate of more than a target frame error rate, the base station can suffer an error propagation due to the 15-times DM symbols received after the full C/I information is transmitted. Accordingly, the 4-bit full C/I information, which is transmitted during the first slot period of each 20 ms frame, is transmitted with a sufficient transmission power so that the corresponding base station can accurately receive the information.
The second transmission mode is the full reporting mode in the normal mode as illustrated in FIG. 1B. In the full reporting mode of the normal mode, the mobile station measures the forward full C/I information of the best serving cell/sector for each 1.25 ms, quantizes the measured information by a predetermined number of bits, and applies a [12, 4]-block coding to the quantized information. Then, the mobile station performs a 8-ary Walsh covering of the best serving cell/sector with respect to the block-coded quantized information, and transmits the Walsh-covered information to at least one base station in an active set including the base stations of the best serving cell/sector.
The full C/I information can be detected and used only by the base stations that can perform a Walsh decovering of the full C/I information. In the full reporting mode of the normal mode, the corresponding base station can detect the quality information of the forward link relatively accurately, but it requires a large amount of transmission power. Thus, it has the disadvantages that it occupies a large capacity of the reverse link. As a result, the full reporting mode of the normal mode will be an improper transmission mode in case that many users exist on the reverse link, and thus it can be used only in case that the reverse load is small.
The third transmission mode is a DM transmission mode in the reduced rate mode as illustrated in FIG. 2A. In the DM mode of the reduced rate mode, the basic operation is the same as that of the DM mode of the first normal mode, but it has the following differences. That is, the number of repetition of the 4-bit full C/I information of the best serving cell/sector transmitted on the first slot for each 20 ms is determined according to a predetermined repetition rate.
For instance, if the repetition rate is 2, the same 4-bit full C/I information is transmitted during the period of the first and second slots. Then, all the DM information is transmitted in the same manner as the DM mode of the normal mode during the period of the third to 16th slots. The full C/I information and the quality up/down command can be detected and used only by the base stations that can perform a Walsh decovering of the full C/I information and the quality up/down command. In the DM mode of the reduced rate mode, which is similar to the full reporting mode of the reduced rate mode, the corresponding base station can accurately receive the 4-bit full C/I information even if a link imbalance occurs in the quality of the reverse link and the forward link.
The fourth transmission mode is the full reporting mode in the reduced rate mode as illustrated in FIG. 2B. In the full reporting mode of the reduced rate mode, the 4-bit full C/I information of the best serving cell/sector is transmitted for each slot in the same manner as the full reporting mode of the normal mode. However, the same 4-bit full C/I information is repeatedly transmitted according to a repetition rate that has been prescribed differently from the DM mode of the reduced rate mode.
If the repetition rate is 2, the 4-bit full C/I information transmitted on the first slot is the same as that transmitted on the second slot. In the same manner, the 4-bit full C/I information transmitted on the third slot is the same as that transmitted on the fourth slot. If the repetition rate is 4, the same 4-bit full C/I information is transmitted on the first, second, third and fourth slots, respectively. The full C/I information can be detected and used only by the base stations that can perform a Walsh decovering of the full C/I information.
If the 4-bit full C/I information is repeatedly transmitted in the above-described manner, the probability that the corresponding base station accurately receives the 4-bit full C/I information can be increased. Accordingly, in the full reporting transmission mode in the reduced rate mode, the corresponding base station can receive the 4-bit full C/I information with an error rate below a target error rate, even in case that the link imbalance occurs between the reverse link and the forward link and the quality of the reverse link deteriorates although the quality of the forward link is good.
A mode to be considered in addition to the above-described four transmission modes is a control hold mode as illustrated in FIGS. 3A and 3B and FIGS. 4A and 4B. This mode is for limiting transmission of a pilot channel and transmission of an CQICH by slots in order to prevent waste of power in case that data to be transmitted on the reverse or forward link does not exist.
It is required that the channel quality information and change information (switching information) on the best serving cell/sector on the Channel Quality Indicator Channel (CQICH) varies depending on the above-described transmission modes on the CQICH. Also, a frame structure of the CQICH should be defined so that the base station may efficiently receive and use the channel quality information and the switching information. For example, as the channel quality information should be continuously updated by the base station and the base station also should schedule mobile stations on the CQICH based on the switching information, the base station should receive the channel quality information without an error or a time delay.